Regulation of growth and somatic embryogenesis by proline and serine in suspension cultures of Dactylis glomerata

Summary The regulatory effects of L-proline and L-serine on growth and somatic embryogenesis of Dactylis glomerata were studied using suspension cultures. Treatments consisted of a factorial arrangement of 4 levels of proline (0-to-50 mM) and 3 levels of serine (0-to-25 mM) in a modified Schenk and Hildebrandt (SH) medium supplemented with 30 αM dicamba (3,6-dichloro-o-anisic acid) (SH-30). Proline amended SH-30 medium resulted in a slight increase in dry weight; however, SH-30 supplemented with serine only dramatically inhibited growth. Growth in media containing mixtures of proline and serine was statistically similar to or less than growth in proline alone or SH-30. Significantly fewer somatic embryos were observed in treatments containing proline or serine alone. Most mixtures of proline and serine stimulated embryogenesis with the optimum response observed with 12.5 mM of each amino acid. Embryos were formed in cultures composed of individual cells and small cell masses. Very little precocious germination was evident. Approximately 70% of the embryos formed in proline-serine treatments germinated and produced seedlings on solidified SH medium without dicamba. The final pH of the media was significantly influenced by the interaction of the amino acids. Treatments with serine alone lowered pH; whereas, proline elevated pH after 6 weeks. Initiation of suspension cultures from somatic embryos was inhibited by media containing serine; whereas, media amended with either proline, casein hydrolysate or SH-30 alone supported good growth of suspension cultures.